1. Field of the Invention
The present invention relates to a frequency offset estimation apparatus and method of an Orthogonal Frequency Division Multiplexing (OFDM) system and, more particularly, to an apparatus and method for estimating a frequency offset which are robust against non-Gaussian noise.
This research was supported by the National Research Foundation (NRF) of Korea under Grants 2012-0005066 and 2012R1A2A2A01045887 with funding from the Ministry of Education, Science and Technology (MEST), Korea, and by the Information Technology Research Center (ITRC) program of the National IT Industry Promotion Agency under Grant NIPA-2012-H0301-12-1005 with funding from the Ministry of Knowledge Economy (MKE), Korea.
2. Discussion of the Related Art
An Orthogonal Frequency Division Multiplexing (OFDM) system is advantageous in that it has high frequency use efficiency and a simple equalizer structure and it is robust against multi-path fading, as compared with the existing single carrier communication system. That is, the OFDM system is being widely used as modulation technology for wireless communication systems owing to high frequency band efficiency and a characteristic robust against multi-path fading and thus has been adopted as the standard of lots of communication system, such as a Digital Subscriber Line (DSL), European Digital Audio and Video Broadcasting (DAB/DVB), IEEE 802.11a, and Hiper-LAN II. Multi-user OFDM technology has been adopted as the IEEE 802.16 standard.
The performance of the OFDM system is very sensitive to a frequency offset that is generated owing to oscillator mismatch or a Doppler phenomenon between a transmitter and a receiver. If a frequency offset exists, orthogonality between sub-carriers is broken and thus interference is generated, with the result that the performance of the OFDM system is severely deteriorated. Accordingly, the estimation of a frequency offset in the OFDM system is one of the most important technical problems that must be solved. Training symbol-based frequency offset estimation which provides better performance than blind-based frequency offset estimation had been taken into consideration.
Conventional frequency offset estimation methods were chiefly proposed assuming that ambient noise is a Gaussian process (Non-patent document 2 to 4). The ambient noise, however, was frequently observed to have a non-Gaussian characteristic in a wireless channel. This is chiefly generated owing to impulse environments resulting from various causes, such as a vehicle ignition device, a moving obstacle, lightning in the air, and reflection of water waves (Non-patent document 5 to 6). The conventional frequency offset estimation methods are problematic in that they have very low performance under the non-Gaussian noise environment because they have been developed on the assumption that embient noise is a Gaussian process.